The increased concern for the inevitable depletion of the oil supply as well as the negative impact of the use of fossil fuels on the environment has highlighted the need for biofuel alternatives such as ethanol, diesel, butanol, hydrogen, and electricity produced from renewable resources. Ideally, a biofuel should have a high energy content and be compatible with the current petroleum-based transportation, storage and distribution infrastructures.
Furthermore, biodiesel can be produced from dedicated agricultural oil feedstocks, such as soybeans, with relatively low inputs and/or minimum impacts on existing agricultural practices, rural economies, and the environment. The economic and environmental viability of the biodiesel industry is, however, limited by the large volumes of glycerol-containing wastewaters generated during production, which most often need to be disposed of for a fee at water treatment facilities. Wastewater with approximately 40-50% of glycerol is generated after the phase separation of the crude biodiesel, but the glycerol is further diluted to ca. 10% after adding wastewater generated from the washing of the crude biodiesel. Glycerol prices have been traditionally high enough to allow producers to generate profit from refining the diluted glycerol waste, concentrating it to a ˜80% stock, and selling it to glycerol biorefineries. However, the rapid growth of the biodiesel industry in the last two decades has produced glycerol in excess of its demand and prices have dropped dramatically. Furthermore, bioethanol production also generates glycerol byproducts up to 10% (w/w) of the total sugar consumed. In this saturated market, glycerol has become a very low-value or a waste product for biodiesel producers and glycerol-containing wastewaters are often an economic and environmental liability to the biodiesel industry.